A fuel injector is believed to deliver fuel at specific time intervals and in precise amounts to intake valves and/or the combustion chamber of an internal combustion engine. It is further believed that fuel flowing through a fuel injector typically exits at a nozzle end of the fuel injector, and that the nozzle end typically has a disk with one or more orifices disposed thereon. It is believed that the resulting spray direction, spray particle size, spray mass flow, and spray pattern from the nozzle are a function of, among other variables, the geometry of the orifices.
An orifice is believed to be formed by drilling through a work piece that can be of any shape, including a flat piece (or disk). There are many known methods of drilling orifices for a fuel injector, including mechanical punching and electric discharge machining (EDM). It is believed that these methods are only capable of forming orifices of 150 to 200 microns in diameter or larger. Moreover, it is also believed that these methods are incapable of forming orifices with entry and exit angles. It is further believed that future low emission standards will require smaller orifices for smaller fuel spray droplets and shorter fuel spray duration. It is therefore believed that it will be technically infeasible and/or cost prohibitive to manufacture orifices using known methods once more restrictive emission standards are adopted.
It is also believed that fuel flow variability from orifices cut using laser beam manufacturing methods is still relatively high. It is further believed that fuel flow variability in laser manufactured orifices is generated, at least in part, by the lack of reproducibility of the orifice entry geometry, or chamfer (i.e., the orifice coefficient is not sufficiently reproducible). In percussion drilling, it is believed that the workpiece and the laser beam are in fixed positions while the pulsed beam impinges on the workpiece. Due to the random nature of metal expulsion, percussion drilling is believed to generate a non-circular orifice or a non-cylindrical orifice. Moreover, it is believed that the inlet geometry is not defined. In trepanning, it is believed that the workpiece is fixed while the laser beam first drills a penetration hole and then spirals out to a desired hole diameter. Helical drilling is similar to trepanning but without the penetration hole. Trepanning or helical drilling is believed to be more precise than percussion drilling, but it is also believed to leave the laser entry side of the orifice undefined.
The present invention provides a laser-machining device that can form a plurality of orifices with chamfers where the orifices are consistent dimensionally, such as, for example, the diameter, the surface roughness, and/or the geometry of the chamfers. In a preferred embodiment, the device includes a laser light source that emits generally coherent light along an axis towards a workpiece. The device also includes a splitter assembly that directs a first portion and a second portion of the generally coherent light about the axis such that at least one orifice and at least one chamfer is formed in the work piece. The device is configured such that it can form at least one orifice and at least one chamfer having a surface roughness of less than two microns and an orifice coefficient ratio of at least 0.6.
The present invention further provides a method of forming a plurality of dimensionally consistent chamfered orifices in a workpiece by a laser light, the orifice being disposed along an orifice axis, and the work piece has a first surface and a second surface. In particular, the method can be achieved by providing at least a first beam and a second beam that are emitted from the laser light source; forming at least one orifice in the work piece by directing at least one of the first and second beams towards the workpiece; and targeting the other of the at least one of the first and second beams to form the at least one chamfer in the at least one orifice to provide for an orifice coefficient of at least 0.6.